libbinder: binders hold wire protocol version

The libbinder wire protocol version is currently unstable, but we may
stablize it. This adds a version field in the stability token which is
passed around with binder objects, so it doesn't require additional
memory.

Future consideration/direction:
- when starting a transaction, attach a binder to a Parcel object
- when parceling, parcel according to the maximum of (locally
  understood wire protocol, binder wire protocol)
- verify in transact the data parcel has the corresponding binder
- when the server creates a reply parcel, note version which is the
  same as the version used in the data Parcel (we know that whoever
  wrote this transaction can understand this level).
- save binary blobs of known write*/read* data flows, and test that
  Parcel can understand and recreate these blobs after it is versioned.

Bug: 167966510
Test: 'atest binderStabilityTest' - verifies behavior
Test: internally checks version is always set
Change-Id: I9bb5be5b5b7d7255f8387cf690d86a055102f95d

1 files changed, 3 insertions, 2 deletions

diff --git a/libs/binder/Parcel.cpp b/libs/binder/Parcel.cpp
index feeb819a8a..cc30fa802a 100644
--- a/libs/binder/Parcel.cpp
+++ b/libs/binder/Parcel.cpp
@@ -171,7 +171,8 @@ status_t Parcel::finishFlattenBinder(
     if (status != OK) return status;
 
     internal::Stability::tryMarkCompilationUnit(binder.get());
-    return writeInt32(internal::Stability::get(binder.get()));
+    auto category = internal::Stability::getCategory(binder.get());
+    return writeInt32(category.repr());
 }
 
 status_t Parcel::finishUnflattenBinder(
@@ -181,7 +182,7 @@ status_t Parcel::finishUnflattenBinder(
     status_t status = readInt32(&stability);
     if (status != OK) return status;
 
-    status = internal::Stability::set(binder.get(), stability, true /*log*/);
+    status = internal::Stability::setRepr(binder.get(), stability, true /*log*/);
     if (status != OK) return status;
 
     *out = binder;